A multifunctional vibration actuator for allowing a single device to perform generation of a ring tone and a body-sensible vibration as an incoming call notification means for portable terminal units represented by portable telephones, has been devised and installed in such portable terminal units.
As shown in FIG. 19, this multifunctional vibration actuator is structured with an approximately cylindrical housing 1 having openings on both sides, a magnetic circuit part in which a pole piece 2 and a yoke 3 are integrally fixed and formed on a magnet 4 so as to form a gap G1 that affects as a magnetic gap, a diaphragm 6 having a voice coil 5 being attached on its surface, and suspensions 7 and 7′ respectively having supporting portions 7a that fixedly support the magnetic circuit part.
One example of the suspensions 7 and 7′, as shown in FIG. 20, includes a ring portion 7a as a supporting portion that fixedly supports the magnetic circuit part, and three arms 7b to 7d being equally spaced (in FIG. 20, equally spaced by 120°) and elongated from an outer shape of the ring portion 7a in the same direction along the outer shape (circular shape in FIG. 20).
By the ring portion 7a of each of the suspensions 7 and 7′ fixedly supporting the magnetic circuit part, and by ends of the arms 7b to 7d being fixed on an inner side surface of the housing 1, the magnetic circuit part is supported with capacity to vibrate in upward and downward directions of FIG. 19 due to deflection of the arms 7b to 7d. More specifically, the suspensions 7 and 7′ with spacer rings 10a and 10b intervening therebetween are fixed by a stopper ring 11, so that the ring portions 7a at the center are engaged with an outer periphery of the yoke 3.
Further, a lead wire of the voice coil 5 is drawn out to an outside of the housing 1 and connected to terminal metal fitting 8 being attached to the outside of the housing 1, and the diaphragm 6 is placed to cover the one opening of the housing 1 so as to arranged the voice coil 5 in the magnetic gap G1. Further, the other opening of the housing 1 is covered by a cover 9 having a through hole 9a, and the cover 9 is fixed thereon.
The multifunctional vibration actuator is assembled to have a clearance G2 that permits deflection of the arms 7b to 7d between the inner side surface of the housing 1 and an outer shape surface of the yoke 3.
When an electrical signal of low frequency band is applied to the voice coil 5 of the multifunctional vibration actuator of such structure, an electromagnetic effect around the magnetic gap G1 causes the magnetic circuit part to vibrate in upward and downward directions of FIG. 19, and this vibration is propagated to an outside of the multifunctional vibration actuator and then notified as a body-sensible vibration to a user of a terminal unit. On the other hand, when an electrical signal of high frequency band is applied, the electromagnetic effect similarly causes the diaphragm 6 to vibrate and generate a sound such as a ring tone or the like, which is then notified to the user.
A characteristic of a body-sensible vibration of this conventional multifunctional vibration actuator, as a characteristic shown by a solid line in FIG. 6, exhibits a sharp, namely, a rapid rise of resonance and a narrow frequency bandwidth in which a desired vibration acceleration can be obtained. Thus, in case a dispersion of a vibration characteristic attributed by manufacturing exists between each multifunctional vibration actuator, or in case an environment of using a terminal unit having the multifunctional vibration actuator changes, the vibration characteristic easily get out of the bandwidth due to the difficulty of determining a resonance point and to the narrow frequency bandwidth in which a desired vibration acceleration can be obtained. Therefore, the desired vibration acceleration is difficult to obtain, and from views of stability and convenience of a vibration characteristic, the conventional multifunctional vibration actuator has room for improvement.
Moreover, when a portable terminal unit having the multifunctional vibration actuator shown in FIG. 19 is in a call waiting status, in other words, the multifunctional vibration actuator is not operating, a shock to an external case of the portable terminal unit causes the magnetic circuit part to vibrate and generate a noise similar to a twang of string, which is represented as a “booming noise” (hereinafter, this noise is referred to as abnormal noise). This abnormal noise causes a user to feel that the external case of the portable terminal unit has insufficient stiffness, or to doubt that installed parts inside the terminal unit are improperly installed or malfunctioning.